1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor element, and in particular a method of manufacturing a light-emitting diode (LED).
2. Description of the Related Art
Light-emitting devices equipped with LED elements are used in, for example, illumination, backlighting and industrial equipment. Efforts are expended to increase the brightness of light-emitting elements in such light-emitting devices. LED elements are manufactured by using, for example, a metal-organic chemical vapor deposition (MOCVD) method to deposit a semiconductor layer of AlGaInP or GaN by epitaxial growth on a GaAs substrate, sapphire substrate or other suitable growth substrates. In an LED element manufactured in this way, light emitted from the light emission layer is absorbed in the growth substrate so that the efficiency of light extraction is reduced. In addition, the efficiency of heat dissipation is poor because of the low thermal conductivity of the growth substrate.
In order to resolve the above-mentioned problems, LED elements are manufactured in the following manner: a semiconductor layer grown on a growth substrate is laminated on a supporting substrate that has high thermal conductivity with a light-reflecting material intervening, and then the growth substrate is removed. Such LED elements are disclosed, for example, in Japanese Patent Application Publication (Kokai) No. 2006-237419.
When semiconductor elements are manufactured using supporting substrates as described above, a eutectic crystal such as AuSn or InAu is used to bond the semiconductor layer to a supporting substrate with high thermal conductivity. This bonding is referred to as “eutectic bonding” in this specification. In eutectic bonding, the eutectic crystal material must be melted or softened at a high temperature (280° C. or above) in order to perform satisfactory bonding with few voids in the bond portion. Further, if there are irregularities in the temperature over the wafer surface, irregularities occur in the melting or softening, and large voids measuring several microns or more occur in the bond portion. Moreover, because treatment must be performed at high temperature, warping of the wafer during bonding due to a difference in the thermal expansion coefficients of the semiconductor layer and the thermally conductive supporting substrate may occur, and destruction of the wafer during subsequent laser liftoff (LLO) of the growth substrate may occur. These result in reduced manufacturing yields and reduced reliability of light-emitting elements manufactured by eutectic bonding.